1. Field of the Invention
This invention relates to a radiation image information detecting panel, which comprises a stimulable phosphor layer capable of storing radiation image information and read-out means for reading out the radiation image information from the stimulable phosphor layer, the stimulable phosphor layer and the read-out means being combined with each other into an integral body.
2. Description of the Related Art
As image recording media for recording radiation images with medical X-ray image recording operations, and the like, stimulable phosphor sheets and electrostatic latent image recording sheets have heretofore been proposed. The stimulable phosphor sheets are capable of storing radiation energy in accordance with radiation image information (with primary stimulation). Also, the stimulable phosphor sheets, on which the radiation energy has been stored, are capable of emitting light in proportion to the amount of the stored energy when the stimulable phosphor sheets are exposed to reading light (with secondary stimulation). The electrostatic latent image recording sheets are capable of recording image information as electrostatic latent images. Also, the electrostatic latent image recording sheets are capable of generating electric currents in accordance with the electrostatic latent images when the electrostatic latent image recording sheets are exposed to reading light.
Ordinarily, in cases where the image information is to be read out from the image recording media, on which the image information has been recorded, the reading light or secondary stimulating rays are irradiated to the image recording media, and the recorded image information is thereby read out.
An image read-out apparatus utilizing a panel-shaped light source as the light source for producing the secondary stimulating rays has been proposed in, for example, U.S. Pat. No. 6,376,857. With the proposed image read-out apparatus, the panel-shaped light source is provided with an electroluminescent layer (hereinbelow referred to as the EL layer) and is combined with an image recording medium, which is of an electrostatic latent image recording type, into an integral body.
With respect to a technique for reading out an image from a stimulable phosphor sheet, a system for performing an image read-out operation by use of a radiation image detecting panel has been proposed in, for example, Japanese Unexamined Patent Publication No. 2000-338297. Such that the time required for image readout may be kept short, such that the apparatus size may be kept small, and such that the cost may be kept low, the radiation image detecting panel is constituted of a stimulable phosphor sheet and a photo-conductor layer, which has an area approximately identical with the area of the stimulable phosphor sheet and has sensitivity with respect to the light emitted by the stimulable phosphor sheet when the stimulable phosphor sheet is exposed to the secondary stimulating rays, the stimulable phosphor sheet and the photo-conductor layer being combined with each other into an integral body. With the system for performing the image read-out operation by use of the radiation image detecting panel as proposed in, for example, Japanese Unexamined Patent Publication No. 2000-338297, the radiation image detecting panel, on which the image information has been recorded, is scanned with spot light in two-dimensional directions, or is linearly scanned with line light, and the image read-out operation is thereby performed. Specifically, the system for performing the image read-out operation as proposed in, for example, Japanese Unexamined Patent Publication No. 2000-338297, is concerned with an image information read-out apparatus, wherein the photo-conductor layer contains a-Se as a principal constituent in order for the weak light emitted by the stimulable phosphor sheet to be detected with a high sensitivity, and wherein an electric field capable of causing avalanche amplification to occur is applied. Also, in, for example, Japanese Unexamined Patent Publication No. 2000-338297, it is described that a surface-shaped light source acting as the secondary stimulating ray source may be combined with the stimulable phosphor sheet into an integral body, and the image read-out operation may be performed through electrical scanning. Further, in, for example, Japanese Unexamined Patent Publication No. 2000-338297, it is described that the photo-conductor layer, which will absorb little red secondary stimulating rays, actually has a slight sensitivity with respect to the red secondary stimulating rays carrying no image information, and that therefore an offset current corresponding to fine electric charges occurring due to the secondary stimulating rays is generated. It is further described therein that, in cases where the secondary stimulating rays are irradiated from the side of the stimulable phosphor sheet, in order for the occurrence of the offset current to be suppressed, a stimulating ray cut-off filter may be inserted between the stimulable phosphor layer and an electrode layer, or between the electrode layer and the photo-conductor layer.
In the image readout from an image information detecting sheet (i.e., an electrostatic recording sheet) of the type, in which the radiation image information is recorded as the electrostatic latent image, as described in, for example, U.S. Pat. No. 6,376,857, the electric current, which occurs within the electrostatic recording sheet due to the irradiation of the reading light to the electrostatic recording sheet, is detected directly. In the image readout from the image information detecting sheet (i.e., the stimulable phosphor sheet) of the type, in which the energy of the radiation is stored, as described in, for example, Japanese Unexamined Patent Publication No. 2000-338297, the light, which is emitted by the stimulable phosphor sheet due to the irradiation of the secondary stimulating rays to the stimulable phosphor sheet, is read out. At the time of the image readout from the stimulable phosphor sheet, the two kinds of light, i.e. the light emitted by the stimulable phosphor sheet and the secondary stimulating rays will mix together. Therefore, in order for the image readout to be performed accurately (i.e., with a high signal-to-noise ratio) by use of the radiation image detecting panel, which comprises the photo-conductor layer and the stimulable phosphor sheet combined with each other into an integral body, in cases where a layer having the sensitivity with respect to the light emitted by the stimulable phosphor sheet is utilized as the photo-conductor layer, it is actually necessary that the secondary stimulating rays and the light emitted by the stimulable phosphor sheet are separated from each other, and that an adverse effect (i.e., the offset current described above) due to the secondary stimulating rays is thereby suppressed.